It has long been recognized that the inclusion of trace amounts of water or small amounts of the lower alcohols in gasoline is advantageous in some respects and deleterious in others. Thus, it has been observed that traces of water contribute to smooth motor performance in conventional spark-ignition engines. Various devices have been developed and employed commercially in fleet operations which inject water vapor into the cylinders along with the air-fuel mixture during stress conditions, such as rapid acceleration or hill climbing to avoid "knock" which is symptomatic of poor efficiency. These devices typically use separate reservoirs of water or water-rich fluids because the water or aqueous fluids have a very low solubility in gasoline at the range of temperatures encountered in both summer and winter driving.
However, the inclusion of trace amounts of water in gasoline in either dissolved or suspended form has also been undesirable for a number of reasons. For example, gasoline saturated with water at ambient temperatures, e.g., 70.degree. F., upon cooling to a lower temperature, e.g., 32.degree. F., can precipitate water either as a liquid or as solid ice causing corrorion, clogged fuel filters, fuel line freeze-up or other malfunctions.
In order to prevent operating difficulties on the part of automobile owners, some refiners add about 1 to 3% of methanol, isopropanol, or other deicers to gasoline so that any water which might separate from the fuel under supersaturated conditions will contain alcohol as an anti-freeze. The addition of de-icers can likewise aggravate the water problem should phase separation into hydrocarbon and aqueous alcohol result.
More recently, for entirely different reasons, there has developed in many areas an incentive or need to include in motor fuels considerably larger amounts of hydrophilic oxycompounds such as methanol, ethanol, acetone and the like. The duel incentive stems from the need to extend available supplies of petroleum and to provide a high octane blending component for lead-free fuels. There is thus incentive to include 5 to 15% or more on a volume basis of such hydrophilic components.
In the United States, the term gasohol typically refers to a blend of 10% by volume ethyl alcohol and 90% by volume unleaded gasoline. However, other percentages and other alcohols, such as methyl and isopropyl, can be used. As used herein, the term gasohol has the broader signification of any blend of a water soluble alcohol or alcohols with a hydrocarbon base fuel.
A gasohol comprised of 10% ethyl alcohol and 90% unleaded gasoline, for example, can be substituted for unleaded gasoline in most cars. Ethyl alcohol has a lower heating value than gasoline, but has a high blending octane number, so that somewhat higher engine compression ratios can be used. The increased engine efficiency obtained when a higher compression ratio is used may offset the reduced heating value of gasohol.
A serious problem with gasohol is that the extremely limited water tolerance of the alcohol component aggravates the phase problem. A relatively small amount of water can cause phase separation in gasohols containing less than 20% alcohol.
The water tolerance of gasoline-alcohol blends depends on the alcohol used, the amount of alcohol in the blend, and on temperature. The greater the concentration of alcohol, the higher is the tolerance for water. For example, the water tolerance of a fuel composition comprising 90% unleaded gasoline and 10% ethyl alcohol is about 0.56 ml. of water per 100 mls. of the blend at 25.degree. C. If the blend contains 5% ethyl alcohol instead of 10%, the water tolerance at 25.degree. C. is not as great--it is only about 0.25 ml. of water per 100 mls. of the blend. If the blend contains 15% ethyl alcohol, the water tolerance at 25.degree. C. is greater--it is about 0.96 ml. of water per 100 ml. of blend.
For a given concentration of alcohol, the tolerance of the blend for water increases with temperature. For example, the water tolerance of a blend of 95% unleaded gasoline and 5% ethyl alcohol is about 0.25 ml. of water per 100 ml. of blend at 25.degree. C., compared to 0.14 ml. of water at 0.degree. C. Similarly, for gasohol containing 10% ethyl alcohol, the water tolerance at 0.degree. C. is only 0.30 ml per 100 ml. of blend, and for gasohol containing 15% ethyl alcohol, the water tolerance at 0.degree. C. is only 0.66 ml per 100 ml. of blend.
There are two major ramifications of the low tolerance of gasohol for water. First, the alcohol used in blending the gasohol must be anhydrous, or nearly anhydrous. Anhydrous ethyl alcohol is significantly more expensive than 90 or 95% ethyl alcohol, and it would therefore be advantageous if the cheaper alcohols could be used. Second, special handling precautions have to be taken to prevent gasohol from coming into contact with water when it is in storage or it is being transported. Resort to on site blending, as opposed to refinery blending, has often been found to be necessary. In addition, gasohol has an increased tendency to cause corrosion, engine starting and operation problems, and fuel line problems due to the difficulty involved in excluding even small quantities of water from automobile fuel tanks in which gasohol is used.
A number of prior patents are directed to liquid fuel mixtures comprised of a hydrocarbon base fuel, water, and an emulsifier. For example, U.S. Pat. No. 3,876,391, U.S. Pat. No. 3,527,581 and U.S. Pat. No. 4,158,551 are directed to such compositions. In some cases, ethoxylated alkylphenols have been disclosed as suitable emulsifiers, or as suitable components in emulsifier mixtures for such compositions. Other prior patents are directed to liquid fuel mixtures comprised of hydrocarbon base fuel, a water soluble alcohol, water, and an emulsifier. For example, U.S. Pat. No. 4,046,519 is directed to such compositions. These prior patents are all directed to compositions that are emulsions or microemulsions. In other words, these patents are directed to compositions in which there are separate aqueous and hydrocarbon phases. While such microemulsions should theoretically be entirely suitable, obvious problems are presented should the emulsions break.
Some investigations have previously been made regarding solubilization of water in pure organic materials such as, for example, cyclohexane, using an ethoxylated nonylphenol mixture. K. Shinoda et al. "Conditions to Produce So-called Microemulsions: Factors to Increase the Mutual Solubility of Oil and Water by Solubilizer," Journal of Colloid and Interface Science, Vol. 42, No. 2, pp. 381-387 (February, 1973). Applicant is not aware, however, of any prior work relating to solubilization of water in gasoline, gasohol, or other hydrocarbon base fuels.
Still further, several prior patents concern the use of various polyethers as gasoline additives for various purposes. U.S. Pat. No. 3,232,724 discloses the addition of an ethoxylated octyl- or nonylphenol containing 4 to 16 ethylene oxide units to gasoline in amounts up to 0.01 weight percent to provide carburetor detergency. U.S. Pat. No. 3,573,001 concerns the use of small amounts of a propoxylated alkanoic acid as a deicer. U.S. Pat. No. 3,440,029 similarly shows an ethoxylated alkylphenol containing 1 to 20 ethylene oxide units employed in small amounts as a deicer. U.S. Pat. No. 2,853,530 illustrates a polyether containing 6 ether groups described as having use in gasoline.